1. Field of the Invention
The invention relates a novel circuit for generating I-Q-signals, suitable for implementation in an Integrated Circuit (IC).
2. Description of the Prior Art
During the past decades electronics have experienced nothing less than a revolution due to the evolution of low cost silicon integrated circuits. Digital circuits have improved so much due to the continuous technology scaling that more and more signal processing is being moved from the analog to the digital domain. Also much of the remaining analog circuitry is being integrated in silicon Integrated Circuits (ICs) instead of being realized as discrete circuits. This development is driven by the possibility of achieving in ICs high density, low cost and in some cases low power. However inductors have been incompatible with silicon IC technology at the frequencies of interest and the functionality of these components has been replaced by active circuits like OPAMPS, transconductors and gyrators. The impact of these developments has been that inductors slowly and almost unnoticed have disappeared from the electronics engineering within many technical fields.
However up to now, phase-shifting circuits have been implemented using resistors and capacitors, mainly because coils have been considered impractical. Modern technology has opened up the possibility of integrating coils in Integrated Circuits; thus making coil based solutions interesting.
Right now two things are happening that change the situation and both are related to the evolution of the silicon IC technology. The first change is that the cheap silicon transistorsxe2x80x94both bipolar and CMOSxe2x80x94are now so fast that radio frequency circuits in the lower GHz range can be made. This has lead to an explosion in the amount of consumer electronics produced and sold in this area. Typical products are cellular phones, pagers, positioning systems, digital television, Internet products, local area networks etc. Many of these electronic circuits can greatly benefit from the use of inductors and transformers for impedance matching, for achieving low noise, to compensate for parasitic capacitances, to get very good linearity and to enable the possibility of having signal swings above the supply. The second change is that the increased transistor speed has moved the focus of the process development to the reduction of the RC delays associated with the IC interconnect. The result is that more and thicker metal layers with lower resistivity are placed further away from the lossy substrate. The impact of this trend is that inductors usable in the lower GHz range can now be integrated. The quality factor is very lowxe2x80x94typically not more than 5xe2x80x94but within the next decade inductors with Q-values of 35 will be available thanks to the continuous technology scaling.
The implications of these changes are that the neglected inductors and transformers, to some extend, will find their way back into the electronics engineering curricula. It also means that many integrated circuit designers who have simply never been taught how to design and use inductors and transformers will overlook valuable circuit solutions. Furthermore there is a whole range of new discoveries to made because integrated circuits have very different properties than the discrete circuits have. Especially the balanced topology, which is problematic in discrete solutions due to higher component count and high relative component tolerances, is much better suited in integrated circuits.
One example of an area that maybe has not be fully understood and investigated is circuits like the cross coupled allpass filter structure that depend on three properties; A) receiving a well balanced signal at the input, B) having well matched components and C) having inductors or transformers as available components. The properties A) and B) have been almost impossible to fulfil prior to the IC era and until now C) has not been compatible with silicon IC technology. Therefore it is only now that all three properties are practically feasible in the same technology.
According to a first aspect of the invention there is provided a polyphase filter for generating an IQ output based upon an input, the filter being included in an Integrated Circuit (IC), and comprises capacitances and inductances, and the capacitances and inductances are integrated into the integrated circuit. Hereby there is provided a LC structure for phase manipulation of balanced signals in state-of-the-art silicon integrated circuit technology. The main benefit of the circuit according to the invention is very low losses compared to the standard phase-shifting circuit using resistors and capacitors. Furthermore the capacitances and the inductances are integrated in the same IC and the circuit in which the filter is used. This increases the integration level of the overall circuit. Until now it has not been possible to use LC components for polyphase filters because the discrete components (especially the inductances) could not be provided with a sufficient precision. However the inventor provided a design guide for inductors in IC""s. This design guide may be used for calculating a specific inductor geometry in order to obtain certain impedance. This design guide is able to provide a sufficient precision for the present purpose.
According to a second aspect of the invention there is provided an IQ generator integrated into an integrated circuit for generating IQ output signal. This generator includes a signal generator providing input with two identical signals opposed in phase, a filter comprises a plurality capacitances and inductances, the capacitances and inductances are integrated into the integrated circuit, and output providing the I and Q signals.
According to a third aspect of the invention a polyphase filter is used in an LC IQ generator integrated into an integrated circuit for generating IQ output signal based upon an input from a signal generator, the filter comprises a plurality capacitances and inductances, and the capacitances and inductances are integrated into the integrated circuit.
According to a fourth aspect of the invention a polyphase filter is used in an IQ generator with transformers, the IQ generator is integrated into an integrated circuit for generating an IQ output signal from the transformers based upon an input from a signal generator, the filter comprises a plurality capacitances and inductances, and the capacitances and inductances are integrated into the integrated circuit.
Furthermore the invention is related to a broad band phase shift circuit that will become very useful is direct conversion receivers. The applicant in the pending application GB 9709464.3 describes a direct conversion concept. The invention has another advantage because it is broad banded so it may work in a plurality of channels and even in more than one frequency band.
The invention may be used for up conversion as well as for down conversionxe2x80x94both in a receiver and a transmitter.